Integrated circuit interconnect structure

ABSTRACT

An integrated circuit (IC) interconnect structure that includes a first via positioned in a dielectric and coupled to a high current device at one end, and a buffer metal segment positioned in a dielectric and coupled to the first via at an opposite end thereof. The buffer metal segment includes a plurality of electrically insulating inter-dielectric (ILD) pads forming an ILD cheesing pattern thereon, to direct current. The IC interconnect structure further includes a second via positioned in a dielectric formed over the buffer metal segment and coupled to the buffer metal segment at one end and a metal power line formed in a dielectric and coupled to the second via at an opposite end thereof. The use of the ILD pads on the buffer metal segment enables a more even distribution of current along the metal power line.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/760,594, filed Apr. 15, 2010, now U.S. Pat. No. 8,237,286, thedisclosure of which is incorporated by reference herein in its entirety.

BACKGROUND

The present invention relates to integrated circuits (ICs), and morespecifically, to an IC interconnect structure having high reliability.

Back-end-of-line (BEOL) interconnects carry high direct current (DC) inadvanced integrated circuit (IC) chip technology. The design of BEOLinterconnects becomes more challenging in advanced technologies. As ICchip technology advances, self-heating by high current devices raisesthe temperature of nearby interconnects under circuit operation andmakes use of high current carrying BEOL interconnects more challenging.For example, a device that uses high current may heat up an interconnectthat is coupled to the device. The high current may causeelectromigration degradation of the interconnect (via and/or line),causing shorts or opens. Typically, the above-described problem has beencircumvented by widening the interconnect carrying the high current.However, severe current crowding may still exist at the via/line contactinterface which is susceptible to electromigration damage.

SUMMARY

Embodiments of the present invention provide an IC interconnectstructure for a high current device that reduces current crowding at ametal layer, to thereby prevent electromigration damage. A designstructure and a method for forming the IC interconnect structure arealso provided.

According to one embodiment of the present invention, an integratedcircuit (IC) interconnect structure is provided. The IC interconnectstructure includes a first via positioned in a dielectric and coupled toa high current device at one end, and a buffer metal segment positionedin a dielectric and coupled to the first via at an opposite end thereof.The buffer metal segment includes a plurality of electrically insulatinginter-dielectric (ILD) pads forming a ILD cheesing pattern thereon, todirect current. The IC interconnect structure further includes a secondvia positioned in a dielectric formed over the buffer metal segment andcoupled to the buffer metal segment at one end and a metal power lineformed in a dielectric and coupled to the second via at an opposite endthereof.

According to another embodiment of the present invention, a designstructure embodied in a machine readable medium for designing,manufacturing, or testing an integrated circuit is provided. The designstructure includes an IC interconnect including a first via positionedin a dielectric and coupled to a high current device at one end and abuffer metal segment positioned in a dielectric and coupled to the firstvia at an opposite end thereof. The buffer metal segment includes aplurality of electrically insulating inter-dielectric (ILD) pads forminga ILD cheesing pattern thereon, to direct current. The IC interconnectfurther includes a second via positioned in a dielectric formed over thebuffer metal segment and coupled to the buffer metal segment at one end,and a metal power line formed in a dielectric and coupled to the secondvia at an opposite end thereof.

According to yet another embodiment of the present invention, a methodis provided. The method includes forming a high current device, forminga first via positioned in a dielectric and coupled to the high currentdevice at one end, forming a buffer metal segment positioned in adielectric and coupled to the first via at an opposite end thereof, andforming a plurality of electrically insulating inter-dielectric (ILD)pads forming a ILD cheesing pattern on the buffer metal segment, todirect current. The method further includes forming a second viapositioned in a dielectric formed over the buffer metal segment andcoupled to the buffer metal segment at one end and forming a metal powerline in a dielectric and coupled to the second via at an opposite endthereof.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a diagram illustrating a top view of an IC interconnectstructure that can be implemented within embodiments of the presentinvention.

FIG. 2 is a diagram illustrating a cross-sectional view of the ICinterconnect structure shown in FIG. 1.

FIG. 3 is a diagram illustrating a top view of an IC interconnectstructure that can be implemented within alternative embodiments of thepresent invention.

FIG. 4 is a cross-sectional view of the IC interconnect structure shownin FIG. 3.

FIG. 5 is a flow diagram of a design process used in semiconductordesign, manufacturing and/or test that can be implemented withinembodiments of the present invention.

DETAILED DESCRIPTION

FIGS. 1 through 4 illustrate integrated circuit (IC) interconnectstructures according to various embodiments of the present invention.Referring to FIGS. 1 and 2, FIG. 1 is a diagram illustrating a top viewof an IC interconnect structure that can be implemented withinembodiments of the present invention, while FIG. 2 is a diagramillustrating a cross-sectional view of the IC interconnect structureshown in FIG. 1. As shown in FIGS. 1 and 2, an IC interconnect structure100 is provided. The IC interconnect structure 100 includes a first via102 positioned in a dielectric 130 b and coupled to a high currentdevice 104 in a dielectric 130 a at one end 102 a, and a buffer metalsegment 108 positioned in a dielectric 130 c and coupled to the firstvia 102 at an opposite end thereof 102 b. The high current device 104may include for example, a transistor, resistor, on-chip heater or anyother device used in an IC that requires high power (e.g., greater than5 milliwatts (mW)). The high current device 104 may be afront-end-of-line (FEOL) level structure or the IC interconnectstructure 100 may be applied at any back-end-of-line (BEOL) layer.

The IC interconnect structure 100 further includes at least one secondvia 112 positioned in a dielectric 130 d formed over the buffer metalsegment 108 and coupled to the buffer metal segment 108 at one end 112 aand a metal power line 114 formed in a dielectric 130 e and coupled tothe second via 112 at an opposite end thereof 112 b.

According to an embodiment of the present invention, the buffer metalsegment 108 is significantly shorter in length than the metal power line114. Also, the buffer metal segment 108 is also equal or shorter inlength than the “Blech length,” so that the metal line is benefited fromthe “short-length effect” and is immune to electromigration because theelectromigration force is balanced by a stress-induced back-flow ofatoms. See I. A. Blech, J. Appl. Phys. 47, 1203 (1976). A Blech length,or L_(Blech), of a conductive material is generally determined by theequation of L_(Blech)=(jL)_(th)/j, wherein (jL)_(th) is the Blechthreshold of the conductive material, and j is a current density passingthrough the conductive material in a direction where the Blech length ismeasured. For most conductive materials including Cu, Au, Ag, and Al,(jL)_(th) is a constant known in the art. For example, the Blechthreshold (jL)_(th) is typically approximately 200 milliamp permicrometer (mA/μm) for copper. The current density can be measured, forexample, in a unit of milliamp per micrometer square (mA/μm²).Therefore, for a current density of for example 20 mA/μm² passingthrough the buffer metal segment 108 consisting essentially of copper,the Blech length may typically be found at approximately 10 micrometers(μm), while the metal power line 114 may be approximately 100micrometers (μm) to carry current over distance.

The buffer metal segment 108 is a short interconnect segment between thefirst via 102 and the metal power line 114 and acts as a “buffer” fortransporting high current so that the interconnect directly contactingthe high current device 104 is protected from electromigration damagebased on a short-length benefit and buffers the device 104 heating andreduces the temperature in the metal power line 114.

Further, as shown in FIG. 1, the buffer metal segment 108 includes aportion having non-parallel sides 116 and 118 wherein a width of thebuffer metal segment 108 varies from one end 108 a to an opposite endthereof 108 b.

According to an embodiment of the present invention, the buffer metalsegment 108 is positioned in a first metal layer 120 of the IC and themetal power line 114 is positioned in a second metal layer 124 of theIC.

According to an embodiment of the present invention, the metal buffersegment 108 and the metal power line 114 may be formed of copper (Cu) oraluminum (Al), for example. The dielectrics 130 a˜130 d may includesilicon, substrate, packaging substrate, silicon nitride (Si3N4),silicon oxide (SiO2), fluorinated SiO2 (FSG), hydrogenated siliconoxycarbide (SiCOH), porous SiCOH, bor-phoso-silicate glass (BPSG),silsesquioxanes, carbon (C) doped oxides that include atoms of silicon(Si), carbon (C), oxygen (0), and/or hydrogen (H), thermosettingpolyarylene ethers, SILK (a polyarylene ether available from DowChemical Corporation), JSR (a spin-on silicon-carbon contained polymermaterial available form JSR Corporation), other low dielectric constant(<3.9) material, or layers thereof, for example. According to anembodiment of the present invention, each dielectric of 130 a˜130 e maybe formed of a different material.

According to an embodiment of the present invention, the buffer metalsegment 108 includes a plurality of electrically insulatinginter-dielectric (ILD) pads 150 forming a ILD cheesing pattern 160thereon, to direct current. According to an embodiment of the presentinvention, the plurality of electrically insulating ILD pads 150 areformed of variable shapes and/or variable density. Also, the pluralityof electrically insulating ILD pads 150 may be part of the dielectric130 c, and they may be formed during the formation of the buffer metalsegment 108.

According to another embodiment of the present invention, as shown inFIG. 1, the ILD cheesing pattern 160 is formed non-uniformly such that adensity thereof is higher at a center region 108 c of the buffer metalsegment 108 and lower near edge portions 108 d along the non-parallelsides 116 and 118.

The buffer metal region 108 separates the metal power line 114 from thefirst via 102 contacting the high current device 104, so that it relaxesthe current density and temperature in the metal power line 114. The ICinterconnect structure 100 reduces local hot spot formation from thehigh current device 104 within the metal power line 114. The ICinterconnect structure 100 also spreads current density distribution inthe metal power line 114 as shown in FIG. 1. Therefore, current crowdingis avoided in the buffer metal segment 108 and the metal power line 114.As indicated by arrows 126, current is diverted closer to the edges 108d of the buffer metal segment 108 such that it is diverted moreuniformly when entering the metal power line 114 as indicated by arrows128.

As mentioned above, the ILD pads 150 may be formed of variable shapesand/or density. FIG. 3 is a diagram illustrating a top view of an ICinterconnect structure that can be implemented within alternativeembodiments of the present invention. FIG. 4 is a cross-sectional viewof the IC interconnect structure shown in FIG. 3. As shown in FIGS. 3and 4, an IC interconnect structure 200 is provided. The IC interconnectstructure 200 includes a first via 202 positioned in a dielectric 230 band coupled to a high current device 204 in a dielectric 230 a at oneend 202 a, and a buffer metal segment 208 positioned in a dielectric 230c and coupled to the first via 202 at an opposite end thereof 202 b.

The IC interconnect structure 200 further includes at least one secondvia 212 positioned in a dielectric 230 d formed over the buffer metalsegment 208 and coupled to the buffer metal segment 208 at one end 212 aand a metal power line 214 formed in a dielectric 230 e and coupled tothe second via 212 at an opposite end thereof 212 b. Further, as shownin FIG. 1, the buffer metal segment 208 includes a portion havingnon-parallel sides 216 and 218 wherein a width of the buffer metalsegment 208 varies from one end 208 a to an opposite end thereof 208 b.

According to an embodiment of the present invention, the IC interconnectstructure 200 further includes ILD pads 250 which form a non-uniformcheesing pattern 260 within the buffer metal segment 208, where anelectrically conductive path near a center region 208 c thereof islengthened by forming a zigzag pattern with irregular cheesing shapes ofthe ILD pads 250. In the current embodiment of the present invention, afirst current path i.e., Path 1 formed along the center region 208 c ofthe metal buffer segment 208) has a same length as a second currentpath, i.e., Path 2 formed along an edge portion 208 d of thenon-parallel sides 216 and 218. For illustration purposes only, FIG. 3only shows Path 2 along the non-parallel side 216. As a result, thecurrent in Path 1 is further spread before entering the metal power line214 such that the current across the width of the metal power line 214more uniformly distributed as indicated by arrows 228.

FIG. 5 is a flow diagram of a design process used in semiconductordesign, manufacturing and/or test. Specifically, FIG. 5 shows a blockdiagram of an exemplary design flow 500 used for example, insemiconductor design manufacturing, and/or test. Design flow 500 mayvary depending on the type of IC being designed. For example, a designflow 500 for building an application specific IC (ASIC) may differ froma design flow 500 for designing a standard component. Design structure520 is preferably an input to a design process 510 and may come from anIP provider, a core developer, or other design company or may begenerated by the operator of the design flow, or from other sources.Design structure 520 comprises an embodiment of the disclosure as shownin FIGS. 1-4 in the form of schematics or HDL, a hardware-descriptionlanguage (e.g., Veriolog, VHDL, C, etc). Design structure 520 may becontained on one or more machined readable medium. For example, designstructure 520 may be a text file or a graphical representation of anembodiment of the disclosure as shown in FIGS. 1-4. Design process 510preferably synthesizes (or translates) an embodiment of the presentinvention as shown in FIGS. 1 through 4 into a netlist 580, wherenetlist 580 is, for example, a list of lines, transistors, logic gates,control circuits, I/O, models, etc. that describes the connections toother elements and circuits in an integrated circuit design and recordedon at least one of a machine readable medium. This may be an iterativeprocess in which the netlist 580 is re-synthesized one or more timesdepending on design specifications and parameters for the circuit.

Design process 510 may include using a variety of inputs; for example,inputs from library elements 530 which may house a set of commonly usedelements, circuits, and devices, including models, layouts, and symbolicrepresentations, for a given manufacturing technology (e.g., differenttechnology nodes, 32 nm, 45 nm, 90 nm, etc.), designed specifications540, characterization data 550, verification data 560, design rules 570,and test data files 585 (which may include test patterns and othertesting information). The design process 510 may further include, forexample, standard circuit design processes such as timing analysis,verification, design rule checking, place and route operations, etc. Oneof ordinary skill in the art of IC design can appreciate the extent ofpossible electronic design automation tools and applications used indesign process 510 without deviating from the scope and spirit of thepresent invention. The design structure of the present invention is notlimited to any specific design flow.

Design process 510 preferably translates the embodiments of the presentinvention as shown in FIGS. 1 through 4, along with any additional ICdesign or data (if applicable, into a second design structure 590. Thedesign structure 590 resides on a storage medium in a data format usedfor the exchange of layout data of ICs (e.g., information stored in aGDSII (GDS2), GL1, OASIS, or any other suitable format for storing suchdesign structures). Design structure 590 may include information such astest data files, design content files, manufacturing data, layoutparameters, lines, levels of metal, vias, shapes, data for routingthrough the manufacturing line, and any other data required by asemiconductor manufacturer to produce the embodiments of the presentinvention as shown in FIGS. 1 through 4. The design structure 590 maythen proceed to a stage 595 where, for example, the design structure590: proceeds to tape-out, is released to manufacturing, is released toa mask house, is sent to another design house, is sent back to thecustomer, etc.

The method as described above is used in the fabrication of integratedcircuit chips, the resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneore more other features, integers, steps, operations, elementcomponents, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the preferred embodiment to the invention had been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

What is claimed is:
 1. A design structure embodied in a machine readablemedium for designing, manufacturing, or testing an integrated circuit,the design structure comprising: an integrated circuit (IC) interconnectincluding: a first via positioned in a dielectric and coupled to a highcurrent device at one end; a buffer metal segment positioned in adielectric and coupled to the first via at an opposite end thereof andthe buffer metal segment comprising a plurality of electricallyinsulating inter-dielectric (ILD) pads formed therethrough; a second viapositioned in a dielectric formed over the buffer metal segment andcoupled to the buffer metal segment at one end; and a metal power lineformed in a dielectric and coupled to the second via at an opposite endthereof; wherein the plurality of ILD pads are configured in a patternwithin a perimeter of the buffer metal segment, with the pads havingvarying shapes and sizes with respect to one another and being arrangedat various densities with respect to locations in the buffer metalsegment so as to spread current density distribution in the metal buffersegment in a manner that avoids current crowding in the metal buffersegment and in the metal power line; and wherein the design structurecomprises a netlist describing the IC interconnect.
 2. The designstructure of claim 1, wherein the buffer metal segment is equal to orshorter than a Blech length and is significantly shorter in length thanthe metal power line.
 3. The design structure of claim 1, wherein thebuffer metal segment is positioned in a first metal layer of the IC andthe metal power line is positioned in a second metal layer of the IC. 4.The design structure of claim 1, wherein the buffer metal segmentincludes a portion having non-parallel sides wherein a width of thebuffer metal segment varies from one end to an opposite end thereof. 5.The design structure of claim 1, wherein the ILD pattern is non-uniformand is formed such that a density thereof is higher at a center regionof the buffer metal segment.
 6. The design structure of claim 1, whereinthe ILD pattern is arranged so as to define a zigzag shaped,electrically conductive path near a center region of the metal buffersection.